Spark plug and method of manufacturing the same



Nov. 11, 1924. 1,515,248

F. M. FURBER SPARK PLUG AND METHOD OF MANUFACTURING THE SAME Filed May 18, 1918 Fig. 5

/NVENTU/-? Y like reference characters any process ofmanufacture,

- ducing this percentage of Patented Nov. 11, 1924.,

FREDERICK MJFURBER, OF REVERE, MASSACHUSETTS.

SPARK PLUG AND METHOD OF MANUFACTURING THE sum.

Application filed May 18, 1918. Serial No. 235,372.

' To all whom it may concern:

Be it known that I, FREDERICK M. FURBER, a citizen of the United States, residing at Revere, in the county of Suffolk and State of Massachusetts, have invented certain Im-' provements in Spark Plugs and Methods of Manufacturing the Same, of which the following description, in connection with the accompanying drawings, is a specification, on the drawings indicating like parts in the several figures.

This invention relates to spark plugs and to methods of manufacturing spark plugs of the general character disclosed in my prior Patent No. 1,228,767 granted June 5, 1917.

The spark plug and method of manufacturing disclosed in said patent have proved very satisfactory in practice andthe present invention aims to devise further improvements both in the construction and also in the methodv of manufacture of the spark plug. \Vhile the process disclosed in said patent produces a very high percentage of marketable plugs, there are, nevertheless, as in a certain percentage of defective plugs, and the present invention is concerned particularly with redefective plugs. To this end the invention involves a novel construction of joint between the upper shoulder of the insulatora-nd the crimped flange that bears on this shoulder, a novel form of flange and a novel method of crimpin th% insulator and referred to. a

The various features of the invention will be readily understood from the following description, reference being made to the accompanying drawings, in which, I

Figures 1, 2, and 3 are cross sectional views on a large scale showing successive steps in the process of turning the flange of the body or shell of the plug over the upper shoulder of the insulator;

Fig. 4 is an angular view of a ring used in making the joint at the upper shoulder;

Fig. 5 is a vertical cross sectional view producing the joint just showing a step in the process of manufac-- ture of the plug, and

Fig. 6' is a view partlynin vertical cross section and partly in front elevation showing the finished plug.

The plug shown comprises a shell or body 2 which may be made out of cold rolled .copper, or other suitable this flange over the upper shoulder of stock of hexagonal cross section, the lower part of this shell or body being turned down to form a shank which is screw threaded to adapt it to be secured in an engine cylinder. The shell is drilled longitudinally to form a. bore therethrough and is counterbored from its outer end, which projects out of the when the plug.- is in use, to form an internal shoulder or seat 4. An insulator 6 is positioned in the bore of the shell 2 and is provided with a circumferential enlargement 7 the" ends of which form upper and lower shoulders 8 and 9, respectively. The shoulder 1 in the shell forms a seat for the lower shoulder 8 of the insulator 6, a gasket 10 being interposed between this seat. and the engine cylinder shoulder. The construction so far described is substantially like that shown in my patent above designated.

In the construction shown in the prior patent the insulator is held in its seat by a flange projecting from the outer end of the shell 2 and crimped over the upper shoulder of the insulator. This feature is also employed in the present construction but the flange 12 is given a different form fromthat formerly used.

According to the preferred process of manufacture the insulator 6 is inserted in the shell 2 with the lower shoulder 9 resting on the gasket 10. A ring 11 made of brass, material, is then placed in the upper end of the bore so that it rests On the shoulder 8 near the junction of this-shoulder with the peripheral surface of the enlargement 7. A

placed on the shoulder 8. Preferably the gaskets used are of the copper asbestos type,

and comprising a well known to the trade, relatively thick sheet of asbestos wrapped in a sheet of copper. The shell 2 with the parts assembled in the manner just described is next placed in a suitable block or fixture and a die A is forceddown onthe gasket 14,

as indicated in Fig. 1, with suflicient pressure to seat the gasket firmly and wedge the ring 11 into the space'between the base of the shoulder 8 and the inner face of the liminary crimping by means of a die B, Fi 2. It will be understood that both the dies A and B preferably are cylindrical in shape so thattheir lower end faces which operate on the work are continuous and that they 10 that is, the end gasket 14 next is flange 12. The flange is next given a prev each perform their operations at a single pressure stroke. The peculiar shape of the lower end of the die B enables it to turn the flange 12 from the position in which it is shown in Fig. 1 into that in which it appears in Fig. 2.

The plug is next set in a suitable fixture such as that indicated in ageneral way in Fig. 5 comprising a block 15 having a. holedrilled therethrou'gh to loosely receive the shank of the shell but supporting the lower shoulder of the shell, this block being pressed upwardly by a strong spring 17 and this upward movement being inturned flange at the upper end of a casing 19 in which the block 15 is mounted. flange turning or crimping operation is completed while the plug is in this fixture. For this purpose a die C may be used, or a construction of the character shown in my prior patent above designated may be employed, the working portion of the die, however, preferably being like that of the die 0 il-* lustrated in the drawings. As best shown in Fig. 3 the lower end of the die has the shape of a wide angled V. This die preferably is cut away, as shown in Fig. 5, so

that it operates simultaneously at diametrically opposite points on the flange 12 and crimps only a relatively small portion of the flange at a time, the die being rotated or indexed between successive strokes so that the points of operation are transferred circumferentially around the'flan'ge until the entire portion of the flange has been turned over into clamping relationship to the insulator. Preferably this operation is performed in substantially the manner described in my prior patent, a predetermined.

pressure being applied to the die so that the flange when finally crimped over exerts substantially a uniform pressure at all points circumferentially of the enlargement of the insulator notwithstanding variations in the height of this enlargement.

The peculiar shape of the die C gives the crimped flange a reverse curve lengthwise of the flange or, in other words, forms a de-' pressioncircumferentially of the crimped flange, as clearly indicated in.Figs. '3 to 6.

This arrangement results in producing a flangeihavingthree distinct parts, as will be seen from Fig. 3, namely, an upright portron which has not. been distorted by the crimpin operation and which may be relatively s ort, another portion extending downwardlyat an abrupt angle to the uprlght portion and extending transversely to .the surface of the upper shoulder 8 of the insulator and a third portion which forms the extreme end part of the flange and which lies substantially parallel to the surface of V the shoulder 8. This last portion forms the insulator clamping part of the flange while the intermediate portion forms what may limited by an The tends to bend the flange outwardly. In the I arrangement shown this pressure is transmitted substantially lengthwise of the intermediate portion of the flange and the peculiar direction and shape of the flange thus enables it to effectually resist the forces 7 tending to bend the flange.

In crimping the flange in the manner just described there obviously is some tendency for the upright portion of the flange to buckle outwardly and in order to counteract this tendency I prefer to confine the flange in a ring D within which the die C reciprocates. This ring fits snugly around the peripheral surface of the flange and is placed in the position in which it is shown in 3 'and 5 before the flange is subjected to the progressive crimping operation of the die C.

It will readily be seen from an inspection of Figs. 3 and 5 that the crimping operation will tend to force the gasket 14 downwardly over the edge of the tapered shoulder 8 and into the space between the peripheral surface of the enlargement 7 and the surface of the bore of the shell. If this action is permitted much of the adv mtage of using a gasket will be lost and the ring 11 is employed to prevent this action. It will readily be seen that this ring effectually confines the gasket against movement toward the base of the shoulder 8 and retains this gasket in its operative position, thus producing a far better joint at the upper shoulder of the insulator than otherwise would be possible. WVhile the upper die C exerts a greater pressure on the insulator clamping portion of the flange than on the intermediate portion which overlies the ring 11 and thus tends to squeeze a certain amount of the asbestos out of the gasket .and force it downwardly along the shoulder, the space into which this material can be forced is so limited by the ring that no substantial shifting movement of the asbestos takes place.

After the crimping operation has been completed the spark plug is removed from the fixture 15, the ring D is knocked off the flange 12 and the other manufacturing operations are completed in any desired manner. Since the present invention a is concerned particularly with the mounting of the insulator in the shell any detailed description of the securing of the unnecessary.

\Vhat is claimed as new, is: 1. A spark plug, comprising a shell having a bore formed therethrough, an insulaelectrodes or the other manufacturing steps is deemed 1 tor positioned in said bore and havin a cir cumferential enlargement with shoulc ers at the opposite ends of said enlargement, a seat in said shell supporting one of said shoulders, and a flange at the outer end of said shell turned inwardly over the other shoulder of said insulator and clamping the insulator in the shell, the inturned portion of said flange being reversely curved in the direction of its length.

2. A spark plug, comprising a shell having a bore formed therethrough, an insulator positioned in said bore and havinga circumferential enlargement with shoulders at the opposite ends of said enlargement, a seat in said shell supporting one of saidshoulders, and a flange at the outer end of said shell turned inwardly over the other shoulder of said insulator and clamping the insulator in the shell, said flange comprising a part lying substantially parallel with the surface of said shoulder, a substantially upright'part, and an intermediate portion adjoining said parts and making an abrupt angle with both of said parts.

3. A spark plug, comprising a shell having a bore formed therethrough, an insulator positioned insaid bore and having a circumferential enlargement with shoulders at the opposite ends of said enlargement, a seat in said shell supportin one of said shoulders, and a flange at t e outerend of said shell turned inwardly over the other shoulder of said insulator and clamping the insulator in the shell, said flange comprising a shoulder clamping portion and a pressure resisting portion joining said clamping portion and extending at such an angle to said shoulder that the presure of the insulator on said flange tending to bend the flange will be transmitted substantially in the direction of the length of said pressure resisting portion.

.4. A spark plug, comprising a shell having a bore formed therethrough, an insulator positioned in said bore and having a circumferential enlargement with tapered shoulders at the opposite-ends of said enlargement, a seat in said shell supporting the lower of said shoulders, a flange at the outer end or said shell turned inwardly over the upper shoulder of the insulator and clamping the insulator in the shell,'-a gasket interposed between said'flange and said upper shoulder, and a ring under said flange confining said gasket against movement downwardly over said upper shoulder on to the peripheral surface of said enlargement.

5. A spark plug, comprising a shell having a bore formed therethrough, an insulator positioned in said bore and having a circumferentia-l enlargement with tapered shoulders at the opposite ends-of said enlargement, a seat in said shellsupporting the upper shoulder of the insulator and clamping the insulatorin the shell, a gasket interposed between said flange and said upper shoulder, and means for limiting the=- movement of said gasket along said shoulder toward the peripheral surface of said enlargement.

-6. That improvement in the method of securing an insulator having a circumferential enlargement. with upper and lower shoulders respectively at the opposite ends of said enlargement, in a spark plug shell having an internal seat for the lower of said shoulders, which consists informing a flange at the outer end of said shell, placing said insulator in the shell, turning said flange inwardly over the upper shoulder of theinsulator into clamping relationship therewith, while the flange is at substantially normal temperatures by acting on a relatively small portion of the flange at a time and with a substantially predetermined force, and confining said flange against outward buckling while it is being.

turned over said shoulder.

I 7. That improvement in the method of per shoulder into clamping relationship therewith while the flange is at substantially normal temperatures by first turning in the upper end portion of the flange and thereafter acting progressively on the inturned flange to force it into its .final clamping position, and confining the flange against outward buckling during said progressive flange turning operation.

8. That improvement in the method of securing an insulator having a circumferential enlargement, witlv upper and lower shouldersrespectively at the opposite ends of said enlargement, in a spark plug shell having an internal seat for the. lower of said shoulders, which consists informing the" shell with a relatively thin annular nge at its outer end, inserting said insulator 1n the shell, placing a gasket on said upper shoulder, placing a ring on said shoulder to fit snugly within the bore of the shell, and then crimping said flange over upon said gasket and ring into position to clamp said insulator in said seat and to cause said flan e to exert a greater clamping pressure on sand gasket than on said ring.

9. That improvement in the method of securing an insulator having a circumferential enlargement, with upper and lower shoulders-respectively at the opposite ends of said enlargement, in a spark plug shell having an internal seat for the lower of said shoulders, which consists in forming the shell with a.relatively thin annular flange at its outer end, inserting said insulator in the shell, and crimping said flange over said.

upper shoulder into clamping relationship therewith while the flange is at substantially normal temperatures by turning in the entire portion of the upper end of the flange and thereafter acting on a relatively small part only of the inturned flange at a time and with a substantially predetermined force to crimp it over said upper shoulder.

10. That improvement in the method of securing an insulator having a circumferential enlargement. with upper and lower shoulders respectively at the opposite ends of said enlargement, in a spark plug shell having an internal seat for the lower of said shoulders. which consists in forming a relatively thin annular flange at the outer end of said shell, placing said insulator in the shell, placing a gasket on said upper shoulder, and then crimping said flange over upon said gasket into position to clamp said insulator in said seat while confining said gasket against movement downwardly along said upper shoulder on to the peripheral surface of said enlargement.

11. That improvement in the method of securing an insulator having a circumferential enlargement, with upper and lower shoulders respectively at the opposite ends of said enlargement, in a spark plug shell having an internal seat for the lower of said shoulders, which consists in forming a relatively thin annular flange at the outer end of said shell, placing said insulator in the shell, placing a gasket on said upper shoulshell turned inwardly over the other shoulder of said insulator and clamping the in-' sulator in the shell, said inturned portion of the flange including a part extending downwardly at an abrupt angle to said shoulder and along which the pressure of the insulator on the flange tending to bend the flange will be transmitted substantially in the direction of the length of said downwardly extending portion.

13. The process herein described which.- consists in providing an electrode insulator with an enlarged flange, placing the flange within a jacket, positioning a die to surround the jacket and engage with an edge portion thereof,-and compressingthe edge portion of the jacket in the direction of its length andinward to provide a turned edge to lock the jacket to the flange.

In "testimony whereof I have signed my name to this specification.

FREDERICK M. FURBER. i 

